Homozygous mutation in KVLQT1 which causes Jervell and Lange Nielsen syndrome

Abstract

Jervell and Lange-Nielsen syndrome (JLN) is an autosomal recessive form of long QT syndrome. In addition to QT interval prolongation, this disorder is associated with congenital deafness. JLN is rare, but affected individuals are susceptible to cardiac arrhythmias with a high incidence of sudden death and short life expectancy. A homozygous mutation in KVLQT1, the potassium channel gene responsible for chromosome 11-linked long QT syndrome, is shown to be a cause of JLN.

What is claimed is: 
     
       1. An isolated DNA fragment or polynucleotide comprising DNA coding for a mutant polypeptide of SEQ ID NO:80 which causes Jervell and Lange-Nielsen Syndrome (JLN) when homozygous. 
     
     
       2. An isolated DNA according to claim 1 wherein said isolated DNA comprises an insertion of a single base between nucleotides 282 and 283 of SEQ ID NO:79. 
     
     
       3. An isolated DNA according to claim 1 wherein said isolated DNA comprises a stop codon at or before nucleotide 564 of SEQ ID NO:79. 
     
     
       4. A nucleic acid probe which will hybridize to the DNA of claim 1 but will not hybridize to DNA encoding a polypeptide of SEQ ID NO:80 under stringent conditions. 
     
     
       5. A nucleic acid probe which will hybridize to the DNA of claim 2 but will not hybridize to DNA encoding a polypeptide of SEQ ID NO:80 under stringent conditions. 
     
     
       6. A method for diagnosing a polymorphism which causes JLN comprising the steps of: a) hybridizing under stringent conditions a probe of claim 4 to a patient's sample of DNA or RNA, and   b) hybridizing under stringent conditions a probe, which hybridizes under stringent conditions to a DNA encoding a polypeptide of SEQ ID NO:80 but not to DNA coding for a polypeptide of SEQ ID NO:80 comprising a mutation which causes Jervell and Lange-Nielsen Syndrome when homozygous, to a patient's sample of DNA or RNA, wherein the presence of a hybridization signal in step (a) but not in step (b) is indicative of the presence of JLN.     
     
     
       7. A method for diagnosing a polymorphism which causes JLN comprising the steps of: a) hybridizing under stringent conditions a probe of claim 5 to a patient's sample of DNA or RNA, and   b) hybridizing under stringent conditions a probe, which under stringent conditions hybridizes to nucleic acid of SEQ ID NO:79 but not to DNA encoding a polypeptide of SEQ ID NO:80 comprising a mutation which causes Jervell and Lange-Nielsen Syndrome when homozygous wherein said DNA encoding a polypeptide of SEQ ID NO:80 comprising a mutation which causes Jervell and Lang-Nielsen Syndrome comprises an insertion of a single base between nucleotides 282 and 283 of SEQ ID NO:79, to a patient's sample of DNA or RNA, wherein the presence of a hybridization signal in step (a) but not in step (b) is indicative of the presence of JLN.     
     
     
       8. A method according to claim 6 wherein the patient's DNA or RNA has been amplified. 
     
     
       9. A method according to claim 7 wherein the patient's DNA or RNA has been amplified. 
     
     
       10. A method according to claim 8 wherein hybridization is performed in situ. 
     
     
       11. A method according to claim 9 wherein hybridization is performed in situ. 
     
     
       12. A method for diagnosing a polymorphism which causes JLN comprising: a) amplifying a portion of a gene or RNA encoding a polypeptide of SEQ ID NO:80 to obtain an amplified portion wherein said portion comprises base 282 of SEQ ID NO:79,   b) measuring the size of said amplified portion, and   c) determining whether an insertion has occurred, wherein the presence of said insertion is indicative of JLN when it is homozygous.     
     
     
       13. A method for diagnosing a polymorphism which causes JLN when a person is homozygous for said polymorphism, said method comprising using a single-stranded conformation polymorphism technique to assay for said polymorphism. 
     
     
       14. The method of claim 13 wherein said polymorphism is an insertion of a single base between nucleotides 282 and 283 of SEQ ID NO:79. 
     
     
       15. A method for diagnosing in a person a polymorphism which causes JLN comprising: a) amplifying a portion of a gene or RNA encoding a polypeptide of SEQ ID NO:80 to produce an amplified portion wherein said portion comprises base number 282 of SEQ ID NO:79, and   b) sequencing said portion wherein an insertion of a single base in both copies of said person's gene or RNA as compared to a gene of SEQ ID NO:79 is indicative of JLN.   
     
     
       16. A method for diagnosing a polymorphism which causes JLN comprising identifying a mismatch between a patient's DNA or RNA and a wild-type DNA or RNA probe wherein said probe hybridizes to the region of DNA encompassing nucleotides 282-283 of SEQ ID NO:79. 
     
     
       17. The method of claim 16 wherein the mismatch is identified by an RNase assay. 
     
     
       18. A cell transfected with the DNA of claim 1. 
     
     
       19. A cell transfected with the DNA of claim 2. 
     
     
       20. A cell transfected with the DNA of claim 3. 
     
     
       21. A cell transfected with RNA encoding human mutant KVLQT1. 
     
     
       22. A cell according to claim 21 wherein said mutant KVLQT1 contains a mutation which results in a stop codon at or before base 564 SEQ ID NO:79. 
     
     
       23. A cell according to claim 22 wherein said mutation is addition of a single base between nucleotides 282 and 283 of SEQ ID NO:79. 
     
     
       24. A method for diagnosing a polymorphism which causes JLN comprising sequencing the KVLQT1 genes in a patient's sample of DNA to determine the presence or absence of a mutation which causes JLN when homozygous. 
     
     
       25. The method according to claim 24 wherein said mutation is insertion of a single base between nucleotides 282 and 283 of SEQ ID NO:79. 
     
     
       26. The method according to claim 24 wherein said patient's sample of DNA has been amplified. 
     
     
       27. The method according to claim 25 wherein said patient's sample of DNA has been amplified. 
     
     
       28. A method for diagnosing a polymorphism which causes JLN comprising sequencing the KVLQT1 RNA in a patient's sample of RNA to determine the presence or absence of a mutation which causes JLN when homozygous. 
     
     
       29. The method according to claim 28 wherein said mutation is insertion of a single base between nucleotides 282 and 283 of SEQ ID NO:79. 
     
     
       30. A method for diagnosing a polymorphism which causes JLN comprising determining the KVLQT1 gene sequence in a patient by preparing cDNA from RNA taken from the patient and sequencing said cDNA to determine the presence or absence of a mutation which causes JLN, wherein if said mutation is homozygous then JLN is present. 
     
     
       31. The method according to claim 30 wherein said mutation is addition of a single base between nucleotides 282 and 283 of SEQ ID NO:79. 
     
     
       32. A nucleic acid vector comprising DNA coding for a mutant human KVLQT1 polypeptide which causes JLN. 
     
     
       33. The vector of claim 32 wherein said DNA comprises an insertion of a single base between nucleotides 282 and 283 of SEQ ID NO:79. 
     
     
       34. A method for diagnosing the presence of JLN wherein said method comprises determining the presence of a mutation in each chromosomal copy of KVLQT1 wherein if a person has a mutation in each copy then said person has JLN.